catch_tostring : moved defintion of rangeToString

Detail::rangeToString is now defined after the various toString
overloads. This results in them being accessible with rangeToString is
instantiated (in this case, by StringMaker<vector>). This (sort-of)
fixes the problem where contained types are toString'd incorrectly.

Consider:
  std::vector<std::string> v { "abc" };

Before:
  Catch::toString( v ) == "{ abc }"
After:
  Catch::toString( v ) == "{ "abc" }"

(note the extra pair of quotes around the "abc" - these are added by
Catch::toString( std::string ) which is now called by rangeToString)

include/internal/catch_tostring.hpp

@@ -101,18 +101,7 @@ struct StringMaker<T*> {
 
 namespace Detail {
     template<typename InputIterator>
-    std::string rangeToString( InputIterator first, InputIterator last ) {
+    std::string rangeToString( InputIterator first, InputIterator last );
-        std::ostringstream oss;
-        oss << "{ ";
-        if( first != last ) {
-            oss << toString( *first );
-            for( ++first ; first != last ; ++first ) {
-                oss << ", " << toString( *first );
-            }
-        }
-        oss << " }";
-        return oss.str();
-    }
 }
 
 template<typename T, typename Allocator>
@@ -238,6 +227,22 @@ inline std::string toString( std::nullptr_t ) {
     }
 #endif
 
+    namespace Detail {
+    template<typename InputIterator>
+    std::string rangeToString( InputIterator first, InputIterator last ) {
+        std::ostringstream oss;
+        oss << "{ ";
+        if( first != last ) {
+            oss << toString( *first );
+            for( ++first ; first != last ; ++first ) {
+                oss << ", " << toString( *first );
+            }
+        }
+        oss << " }";
+        return oss.str();
+    }
+}
+
 } // end namespace Catch
 
 #endif // TWOBLUECUBES_CATCH_TOSTRING_HPP_INCLUDED